The present invention relates to a function-preset wiring device for automobiles, and more particularly to an improved device for forming a through circuit by which signals from a junction block (hereinbelow, abbreviated to "J. B.") are externally delivered via an electronic unit detachably connected to the J. B.
Heretofore, for the electric wiring of an automobile, a J. B. in which a large number of electronic components such as relays and fuses are intensively disposed has been used to facilitate the fabrication of wire harnesses and to simplify a wiring form. Since, however, the number of the components of car electronics tends to increase year by year from the aspects of enhancements in the safety and comfortable ride and drive of the automobile, the J. B. enlarges in size and the internal circuit arrangement thereof becomes complicated. Moreover, since the structure of the J. B. is necessarily different according to the sorts and grades of automobiles, various kinds of J. B.'s need to be prepared at all times and the production and administration thereof expend a long time and much labor. Therefore, a system has been adopted wherein a basic circuit irrespective of the sorts, grades etc. of automobiles is included in a J. B. in built-in fashion, and wherein an electronic unit in which functional circuits such as a defogger, lamp control unit and a power window control unit to be selected depending upon the sorts, grades etc. of automobiles are set, is detachably connected to the J. B.
Such electronic unit is naturally equipped with a through circuit in order to have a connecting function. The through circuit is used within the unit and also extends outside it.
The formation of the through circuit will be more concretely described with reference to the drawings. In FIG. 6, numeral 30 designates a J. B. in which a bus bar circuit plate (not shown) having a desired circuit arrangement is mounted. Numeral 31 designates an electronic unit, which is provided with a J. B. coupling connector portion 33 and an external coupling connector 34 at an outer periphery of a case 32 and which receives therein a printed circuit plate 36 carrying electronic elements 35a, 35b such as resistors, capacitors, and an IC or LSI. A branch terminal 37 is fixed to a part of the circuit of the printed circuit plate 36 perpendicularly thereto by soldering, and an elongated tab terminal 38 which is erected from the bus bar of the bus bar circuit plate and formed as a continuous part thereof protrudes into the external coupling connector 34 while penetrating the printed circuit plate 36 as well as the branch terminal 37, thereby to form a through terminal for externally connecting the internal circuit of the J. B. 30. As shown in FIG. 7, the branch terminal 37 has a structure wherein the free edges of upright side walls 37b on both the sides of a base plate 37a are bent toward the base plate, and an embracing portion 37c for the tab terminal 38 is formed by the bent parts and the base plate 37a, and wherein an elastic contact piece 37d is folded back and formed from one end of the base plate 37a, while a connecting pin 37e is protrusively provided at the other end. The connecting pin 37e is fixed to the circuit of the printed circuit plate 36.
The through circuit described above is constructed of the branch terminal 37 fixed to the printed circuit plate 36, and the tab terminal 38 extended from the J. B. 30. Since, however, the tab terminal 38 is comparatively long and the branch terminal 37 has the rigid body structure, the connection position of the tab terminal 38 as the through terminal is to be strictly regulated.
In the presence of a drawback such as inclination or float at the stage of fixing the branch terminal 37 to the printed circuit plate 36, or in the presence of any deformation or warp of the branch terminal itself or the dimensional error of the printed circuit plate, the connection of the branch terminal 37 with the through terminal 38 becomes difficult. An offset attributed to unreasonable connection acts as an external force on another connection portion (a male terminal at the external coupling connector 34), so that a normal fitted state is not established, and the electrical connection becomes unstable. Moreover, since the through terminal 38 is elongate, the positioning dimensions of terminal inserting holes 30a, 34a, etc. to be formed in the J. B. 30, the electronic unit 31, etc. need to be exact, and a long time is expended for the assemblage of the J. B. and the electronic unit.